Long Term Evolution (LTE)/LTE-Advanced (LET-A) technology is a main trend of the 4th Generation mobile communication technology (4G). LTE/LTE-A is divided into the following two different division duplex modes: Frequency Division Duplex (FDD) and Time Division Duplex (TDD). A frame structure of FDD is referred to as Frame structure type 1, and a frame structure of TDD is referred to as Frame structure type 2.
FIG. 1 is a schematic diagram of the Frame structure type 1 in related art. As shown in FIG. 1, the Frame structure type 1 is described below. Each radio frame has a length Tf=307200×Ts=10 ms, and is composed of 20 slots each having a length Tslot=15360×Ts=0.5 ms. Serial numbers of the 20 slots are from 0 to 19. Ts is a time unit, Ts=1/(15000×2048) second. A subframe is defined to include two consecutive slots, ie, a subframe i includes slots 2i and 2i+1. For FDD, in an interval of 10 milliseconds, 10 subframes are used for a downlink transmission, 10 subframes are used for a uplink transmission, and the downlink transmission and the uplink transmission are performed at different frequencies respectively. In a half-duplex FDD, a user equipment (UE) cannot perform transmission and reception simultaneously. In the full duplex FDD, there is no such restriction.
FIG. 2 is a schematic diagram of the Frame structure type 2 in related art. As shown in FIG. 2, the Frame structure type 2 is described below. Each radio frame has a length Tf=307200×Ts=10 ms, and is composed of 2 half-frames. Each half-frame has a length 153600×Ts=5 ms. Each half-frame includes 5 subframes. Each subframe has a length 30720×Ts=1 ms. Each subframe is defined to include two slots, ie, a subframe i includes slots 2i and 2i+1. The slot has a length Tslot=15360×Ts=0.5 ms. Ts is a time unit, Ts=1/(15000×2048) second.
Changes in uplink-downlink configuration of a cell occur between frames. Uplink-downlink transmission occurs on subframes of the frames. The uplink-downlink configuration of the current frame is obtained from high level signaling.
The uplink-downlink configurations shown Table 1 have 7 types. For each subframe of a radio frame, “D” marks a downlink subframe for the downlink transmission. “U” marks an uplink subframe for the uplink transmission. “S” marks a special subframe. As shown in Table 1, the special subframe has three regions: a downlink pilot time slot (DwPTS), a guard period (GP), and a uplink pilot time slot (UpPTS).
TABLE 1Downlink-Uplink-to-UplinkdownlinkSwitch-Con-pointfigurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
The downlink transmission of the LTE/LTE-A technology uses an Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. Data is modulated on the subcarrier of frequency domain, and then is converted to time domain and added with a cyclic prefix to form a complete OFDM symbol transmitted in time domain. The cyclic prefix (CP) is used for resisting a symbol interference in time domain and an inter-subcarrier interference in frequency domain which are generated by multipath. In the LTE/LTE-A system, there are two CPs with two lengths. One is a normal cyclic prefix (NCP), and the other one is an extended cyclic prefix (ECP). The extended CP is used in a scenario where the multipath delay spread is greater. In the NCP case, a subcarrier interval is 15 kHz. In the ECP case, there are two subcarrier intervals: 15 kHz and 7.5 kHz.
Each signal transmitted in the slot is represented by one or more resource grid. The resource grid is composed of NRBDL*NscRB subcarriers and NsymbDL OFDM symbols. NRBDL denotes the number of physical resource blocks (PRBs) or resource blocks (RBs). NscRB denotes the number of subcarriers in the resource blocks. NRBDL denotes the number of OFDM symbols in the slot. Parameters of the physical resource block are illustrated in Table 2. The number of subcarriers and the number of OFDM symbols in one RB are shown in Table 2. Parameters of the OFDM symbol are illustrated in Table 3. The length of the cyclic prefix is illustrated in Table 3.
TABLE 2ConfigurationNscRBNsymbDLNCPΔf = 15 kHz127ECPΔf = 15 kHz6Δf = 7.5 kHz243
TABLE 3ConfigurationCP length NCP, lNCPΔf = 15 kHz160 for l = 0144 for l = 1, 2, . . . , 5ECPΔf = 15 kHz512 for l = 0, 1, . . . , 5Δf = 7.5 kHz1024 for l = 0, 1, 2
The number NRBDL of the physical resource blocks is determined by a downlink transmission bandwidth configured by a cell, and has a minimum value of 6 and a maximum value of 110.
PRBs in two consecutive slots of a same subframe are a same one, and are referred to as a PRB pair.
FIG. 3 is a schematic diagram of a downlink resource grid in the related art. As shown in FIG. 3, each unit in the resource grid is referred to as a resource element (RE), and labeled by an index pair (k,l), where k=0, . . . , NRBDL*NscRB−1, and l=0, . . . , NsymbDL−1. k denotes a sequence number of the subcarrier in the frequency domain, and l denotes a sequence number of the OFDM symbol in the time domain.
The antenna port is defined as a channel through which a symbol transmitted via this antenna port passes. The antenna port can be inferred from the channel through which other symbols are transmitted via this same port. An antenna port also is defined with a corresponding sequence number for being distinguished from other antenna ports and for indexing the antenna port.
The downlink physical channel corresponds to sets of resource elements for carrying information from upper layers. Downlink physical information includes: a Physical Downlink Shared Channel (PDSCH), a Physical Multicast Channel (PMCH), a Physical Broadcast Channel (PBCH), and a physical control format, a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid ARQ Indicator Channel (PHICH), and an enhancement Physical Downlink Control Channel (EPDCCH).
A downlink physical signal corresponds to a set of resource elements, and is used by a physical layer and is not used for carrying the information from upper layers. The downlink physical signal includes a reference signal (RS), a synchronization signal, and a discovery signal.
The reference signal is also referred to as a pilot frequency, and is of the following types: a Cell-specific Reference Signal (CRS), a Multimedia Broadcast Single Frequency Network (MB SFN) reference signal (MB SFN reference signal), a UE-specific Reference Signal (Demodulation Reference Signal (DMRS)), a Positioning reference signal, and a Channel State Information (CSI) reference signal (CSI-RS). There are two types of UE-specific reference signals: UE-specific reference signals associated with PDSCH and Demodulation reference signals associated with EPDCCH.
The channel state information reference signal (CSI-RS) is used by a terminal for predicting the channel state. The CSI-RS transmitted with non-zero power is referred to a non-zero power CSI-RS (NZP CSI-RS). Sometimes, in order to avoid interference generation, data transmission on some REs on the PDSCH needs to be avoided, so CSI-RS is transmitted with zero power, which is referred to as zero power CSI-RS (ZP CSI-RS) in this case. The corresponding set of resource elements is zero power CSI-RS resources. Sometimes, in order to measure interference, the CSI-RS is transmitted with zero power. In this case, the corresponding set of resource elements is referred to as Channel-State Information—Interference Measurement Resource (CSI-IM Resource).
CSI reference signal configuration is used for indicating the RE mapped by the CSI-RS, that is, the RE used in the CSI-RS transmission. The sequence number of the CSI-RS configuration is used for distinguishing different CSI-RS configurations. The set of REs of the CSI-RS in a configuration in which one CSI-RS is transmitted or mapped is referred to as a CSI-RS resource pattern. The CSI reference signal subframe configuration is used to indicate the subframe where the CSI-RS transmission is located.
A kind of CSI-RS configuration is a CSI-RS configuration with a certain number of antenna ports, for example, a CSI-RS configuration with an antenna port quantity of 8 and a configuration number of 0. A kind of CSI-RS resource pattern is a CSI-RS resource pattern with a certain number of antenna ports, for example, a CSI-RS resource pattern with an antenna port quantity of 8 and an index number of 0.
The set of REs of CSI-RSs transmitting or mapping a part of ports in a CSI-RS configuration is referred to as a partial port pilot resource pattern, for example, a port pilot resource pattern with port number {15, 16, 17, 18}.
An existing art supports CSI-RSs with a port quantity of 1, 2, 4, and 8, and the CSI-RS resource patterns with such port quantities are repeated on each PRB pair in the bandwidth range on the transmission subframe.
The RE sets of the CSI-RS resource patterns with different port quantities in all configuration are the same, that is, the RE set of the CSI-RS resource pattern with the port quantity of 2 in all configuration is the same as the RE set of the CSI-RS resource pattern with the port quantity of 4 in all configuration. For example, for a CSI-RS configuration which is common to the frame structure type 1 and the frame structure type 2, the RE sets of the CSI-RS resource patterns with different port quantities in all configuration are the same, and the number of REs on a PRB pair is 40.
FIG. 4 is a schematic diagram of a resource pattern of a CSI-RS with the number of ports being 4 on a RB pair in the related art. FIG. 5 is a schematic diagram of a resource pattern of a CSI-RS with the number of ports being 8 on a RB pair in the related art.
In order to make full use of power and improve the accuracy of channel measurement, the CSI-RSs of various ports are further divided into groups, that is, a group includes CSI-RSs of multiple ports, and there are one or more groups with different numbers. The CSI-RSs of each port in the group are mapped to a group of common REs in a code division multiplexing manner. For example, the number of ports in the group is N, the CSI-RS sequence is {r0, r1, . . . , rN-1}. There is another sequence group {w0p, w1p, . . . , wN-1p} of length N where p=K+0, K+1, . . . , K+N−1, and there are N sequences in the group, the sequences in the group are orthogonal to each other, that is, Σm=0N-1wmiwmj=0, where i, j=K+0, K+1, K+N−1, and i≠j. The CSI-RS sequence {r0, r1, . . . , rN-1} modulates the sequence {w0p, w1p, . . . , wN-1p} to obtain the CSI-RS sequence {r0w0pr1w1p, . . . , rN-1wN-1p} of the port p, which corresponds to a group of common REs, and each element in the CSI-RS sequence of the port p is mapped to the REs one by one, where N is the length of multiplexing.
In an existing art, the CSI-RS multiplexing between ports is mapped to the RE in the following manner: ports are divided into groups, for example, ports are divided into four groups: {15, 16}, {17, 18}, {19, 20}, {21, 22}; the frequency division manners among these four groups are multiplexed on RE, and the CSI-RSs on the ports in the groups multiplexed to the REs in the time domain by code division, for example, the CSI-RS of the port 15 and the CSI-RS of the port 16 are multiplexed in the time domain in code division manner.
The base station informs the terminal of information of CSI-RS resource through upper layer signaling. The information includes CSI-RS resource configuration identity, the number of CSI-RS ports, CSI-RS configuration, and CSI-RS subframe configuration.
The CRS can be used not only for the measurement of the channel state but also for receiving the estimation of the channel coefficient during demodulation. However, as the number of ports increases, the overhead increases drastically. Therefore, when the number of ports is 8, the CRS is no longer used to measure the channel state, and the CSI-RS with low pilot density and low overhead is used instead. However, with the development of technologies and requirements, there is a need to further develop technologies for a larger number of antenna-terminated applications, such as the number of ports of 12, 16, and the like, which involves the channel state measurement of these larger numbers of ports. The current method of transmitting the channel measurement pilot with a large number of ports is aggregating multiple measurement pilots with small number of ports. For example, CSI-RS using K N-ports aggregates CSI-RS of K*N ports, where * is a multiplication sign. For example, (N, K)=(8,2) aggregates the CSI-RS of 16 ports.
However, after aggregation, the sorting rule of the reference signal ports or the reference signal port numbers has a great influence on the performance of channel measurement feedback. The position relationship or polarization property relationship between the antenna ports is different, and the corresponding channel coefficient relationship characteristics are not the same. The relationship between the codeword elements reflects the relationship between the port channel coefficients and also reflects the position relationship or polarization property relationship between antenna ports.
With respect to the above problems in related technologies, there is currently no effective solution.